A continuously variable transmission called an “IVT (Infinity Variable Transmission)” is known which converts a rotational movement of an output shaft of an engine into a swing movement and further converts the swing movement into a rotational movement to output the resulting movement from an output shaft of the transmission. In a transmission of this type, a transmission ratio can be varied in a stepless manner without the use of a clutch, and a maximum value of the transmission ratio can be set to infinity. Note that in such a transmission, an output speed obtained when the transmission ratio is set to infinity is zero.
FIG. 4 is a side cross-sectional view illustrating a structure of part of a continuously variable transmission which is called an “IVT”, as viewed in an axial direction thereof. The continuously variable transmission illustrated in FIG. 4 includes: an input shaft 101 that rotates around an input center axis O1 by receiving rotational power from a power source such as an internal combustion engine; an eccentric disk 104 that rotates together with the input shaft 101; a connection member 130 through which an input side and an output side are connected to each other; and a one-way clutch 120 provided at the output side.
The eccentric disk 104 is formed into a circular shape, with a first supporting point O3 located at its center. The first supporting point O3 is set so that the eccentric disk 104 rotates together with the input shaft 101 around the input center axis O1 while an eccentricity r1 variable with respect to the input center axis O1 is maintained. Accordingly, the eccentric disk 104 is set so that the eccentric disk 104 rotates eccentrically in accordance with a rotation of the input shaft 101 around the input center axis O1 while the eccentricity r1 is maintained.
As illustrated in FIG. 4, the eccentric disk 104 includes: an outer disk 105; and an inner disk 108 that is integral with the input shaft 101. The inner disk 108 is formed into a thick disk whose center is deviated by a given eccentricity distance with respect to the input center axis O1 serving as a center axis of the input shaft 101. The outer disk 105 is formed into a thick disk whose center is the first supporting point O3, and includes a first circular hole 106 whose center is deviated from the center of the outer disk 105 (i.e., the first supporting point O3). An outer periphery of the inner disk 108 is rotatably fitted to an inner periphery of the first circular hole 106.
The inner disk 108 is provided with a second circular hole 109 whose center is the input center axis O1 and whose peripheral portion is partially opened toward the outer periphery of the inner disk 108. A pinion 110 is rotatably contained inside the second circular hole 109. Through openings at an outer periphery of the second circular hole 109, teeth of the pinion 110 intermesh with an internal gear 107 provided at the inner periphery of the first circular hole 106 of the outer disk 105.
The pinion 110 is provided so as to be rotated coaxially with the input center axis O1 serving as the center axis of the input shaft 101. In other words, a rotation center of the pinion 110 coincides with the input center axis O1 serving as the center axis of the input shaft 101. The pinion 110 is rotated inside the second circular hole 109 by an actuator. In normal times, using, as a reference, a speed at which a rotation of the pinion 110 is synchronized with that of the input shaft 101, a speed which is above or below a speed of the input shaft 101 is given to the pinion 110, thus causing a relative rotation of the pinion 110 with respect to the input shaft 101. For example, when the pinion 110 and an output shaft of an actuator 180 are arranged so as to be connected to each other and a rotation difference occurs between a rotation of the actuator 180 and that of the input shaft 101, a speed reducing mechanism (e.g., a planetary gear) is used to change a relative angle between the input shaft 101 and the pinion 110 by a value obtained by multiplying the rotation difference by a speed reducing ratio, thus enabling the relative rotation of the pinion 110 with respect to the input shaft 101. In this case, the eccentricity r1 does not change when there is no rotation difference between the actuator 180 and the input shaft 101 and the rotations thereof are synchronized.
Accordingly, the rotation of the pinion 110 causes the internal gear 107 with which the teeth of the pinion 110 intermesh, i.e., the outer disk 105, to rotate relatively with respect to the inner disk 108, thus changing a distance (i.e., the eccentricity r1 of the eccentric disk 104) between the center of the pinion 110 (i.e., the input center axis O1) and the center of the outer disk 105 (i.e., the first supporting point O3).
In this case, settings are made so that the rotation of the pinion 110 can allow the center of the outer disk 105 (i.e., the first supporting point O3) to coincide with the center of the pinion 110 (i.e., the input center axis O1), and the eccentricity r1 of the eccentric disk 104 can be set to “zero” by allowing the center of the outer disk 105 and the center of the pinion 110 to coincide with each other.
The one-way clutch 120 includes: an output member (clutch inner) 121 that rotates around an output center axis O2 located away from the input center axis O1; a ring-like input member (clutch outer) 122 that swings around the output center axis O2 by receiving power in a rotational direction from outside; and a plurality of rollers (engagement members) 123 inserted between the input member 122 and the output member 121 so as to put the input member 122 and the output member 121 into a locked state or an unlocked state. Note that the one-way clutch 120 is provided with the rollers 123, the number of which corresponds to the number of sides of the output member 121 in a cross section thereof.
Power (torque) is transmitted from the input member 122 of the one-way clutch 120 to the output member 121 thereof on the condition that a rotational speed of the input member 122 in a forward direction (i.e., a direction indicated by an arrow RD1 in FIG. 4) exceeds a rotational speed of the output member 121 in the forward direction. Specifically, in the one-way clutch 120, it is not until the rotational speed of the input member 122 exceeds the rotational speed of the output member 121 that the input member 122 and the output member 121 are engaged (locked) with each other via the rollers 123, and swing power of the input member 122 is converted into a rotational movement of the output member 121.
A projected portion 124 is provided at one peripheral position of the input member 122, and the projected portion 124 is provided with a second supporting point O4 located away from the output center axis O2. A pin 125 is disposed on the second supporting point O4 of the input member 122, and a tip (other end) 132 of the connection member 130 is rotatably connected to the input member 122 via the pin 125.
The connection member 130 includes a ring portion 131 at its one end. An inner periphery of a circular opening 133 of the ring portion 131 is rotatably fitted to an outer periphery of the eccentric disk 104 via a bearing 140. Accordingly, the one end of the connection member 130 is rotatably connected to the outer periphery of the eccentric disk 104 while the other end of the connection member 130 is rotatably connected to the second supporting point O4 provided on the input member 122 of the one-way clutch 120 in the above-described manner, thus providing a four joint link mechanism in which four joints, i.e., the input center axis O1, the first supporting point O3, the output center axis O2 and the second supporting point O4, function as points of rotation as illustrated in FIG. 5.
FIG. 5 is an explanatory diagram illustrating principles of driving force transmission in a continuously variable transmission provided as the four joint link mechanism. In the four-joint link mechanism, a rotational movement given to the eccentric disk 104 from the input shaft 101 is transmitted, as a swing movement of the input member 122, to the input member 122 of the one-way clutch 120 via the connection member 130, and the swing movement of the input member 122 is converted into a rotational movement of the output member 121. A single rotation of the input shaft 101 which rotates the eccentric disk 104 causes a single reciprocating swing of the input member 122 of the one-way clutch 120. As illustrated in FIG. 5, irrespective of the value of the eccentricity r1 of the eccentric disk 104, a swing cycle of the input member 122 of the one-way clutch 120 always remains constant. An angular velocity ω2 of the input member 122 is determined by a rotational angular velocity ω1 of the eccentric disk 104 (input shaft 101) and the eccentricity r1 thereof.
In this case, in a transmission ratio variable mechanism 112 including: the pinion 110; the inner disk 108 that includes the second circular hole 109 in which the pinion 110 is contained; the outer disk 105 that includes the first circular hole 106 in which the inner disk 108 is rotatably contained; and the actuator 180, the eccentricity r1 of the eccentric disk 104 can be changed by moving the pinion 110 by the actuator 180. By changing the eccentricity r1, a swing angle θ2 of the input member 122 of the one-way clutch 120 can be changed, thus making it possible to change a ratio of a speed of the output member 121 to that of the input shaft 101 (i.e., a transmission ratio i). In other words, an adjustment to the eccentricity r1 of the first supporting point O3 with respect to the input center axis O1 changes the swing angle θ2 of a swing movement transmitted to the input member 122 of the one-way clutch 120 from the eccentric disk 104, thus making it possible to change the transmission ratio obtained when rotational power inputted to the input shaft 101 is transmitted to the output member 121 of the one-way clutch 120 via the eccentric disk 104 and the connection member 130.
FIGS. 6A to 6D and FIGS. 7A to 7C are explanatory diagrams illustrating principles of speed change effected by the transmission ratio variable mechanism 112 in the continuously variable transmission illustrated in FIG. 4. As illustrated in FIGS. 6 and 7, the pinion 110 of the transmission ratio variable mechanism 112 is rotated to rotate the outer disk 105 with respect to the inner disk 108, thus making it possible to adjust the eccentricity r1 of the eccentric disk 104 with respect to the input center axis O1 (i.e., the rotation center of the pinion 110).
For example, as illustrated in FIG. 6A and FIG. 7A, when the eccentricity r1 of the eccentric disk 104 is set to “LARGE”, the swing angle θ2 of the input member 122 of the one-way clutch 120 can be increased, and therefore, the low transmission ratio i can be achieved. As illustrated in FIG. 6B and FIG. 7B, when the eccentricity r1 of the eccentric disk 104 is set to “INTERMEDIATE”, the swing angle θ2 of the input member 122 of the one-way clutch 120 can be set to “INTERMEDIATE”, and therefore, the intermediate transmission ratio i can be achieved. As illustrated in FIG. 6C and FIG. 7C, when the eccentricity r1 of the eccentric disk 104 is set to “SMALL”, the swing angle θ2 of the input member 122 of the one-way clutch 120 can be reduced, and therefore the high transmission ratio i can be achieved. As illustrated in FIG. 6D, when the eccentricity r1 of the eccentric disk 104 is set to “ZERO” or set below a minimum value, the swing angle θ2 of the input member 122 of the one-way clutch 120 can be set to “ZERO” or “MINIMUM”, and therefore, the transmission ratio i can be set to “INFINITY (∞)”. Note that the minimum eccentricity r1 is the smallest eccentricity when rotational power inputted to the input shaft 101 is transmitted to the output member 121 of the one-way clutch 120 in the continuously variable transmission.
When the eccentricity r1 is zero in the transmission ratio variable mechanism 112 of the continuously variable transmission, the swing angle θ2 of the input member 122 of the one-way clutch 120 is zero. When the eccentricity r1 is greater than zero and smaller than the minimum value, the input member 122 swings at the very small swing angle θ2. However, the swing movement in this case is absorbed by a torsion characteristic of the rotors 123 which will be described later, and is therefore not transmitted to the output member 121. Accordingly, not only when the eccentricity r1 is zero but also when the eccentricity r1 is smaller than the minimum value, the transmission ratio i is eventually set to “INFINITY (∞)”.
FIG. 8 is a cross-sectional view of the one-way clutch 120, a portion of which is enlarged. FIGS. 9A to 9C are partially enlarged views of the one-way clutch 120 in respective states. As illustrated in FIG. 8 and FIGS. 9A to 9C, a surface of the output member 121 which comes into contact with the rollers 123 includes dents along which the rollers 123 are movable in a swing direction in accordance with the swing movement of the input member 122. Note that depths of the dents vary depending on whether the input member 122 is moved in an idle direction or in a torque transmission direction illustrated in FIG. 8, and the depth of the dent at the position in the idle direction is deeper than that of the dent at the position in the torque transmission direction.
When the input member 122 swings in the idle direction relatively with respect to the output member 121, the rollers 123 also move in the idle direction. Space extending from the input member 122 to the output member 121 at the position in the idle direction is slightly larger than a size of each roller 123. Hence, the roller 123 that has moved to this position runs idle. On the other hand, when the input member 122 swings in the torque transmission direction relatively with respect to the output member 121, the rollers 123 also move in the torque transmission direction. Space extending from the input member 122 to the output member 121 at the position in the torque transmission direction is slightly smaller than the size of each roller 123. Hence, the roller 123 that has moved to this position is sandwiched between the input member 122 and the output member 121 and thus receives pressure in opposite directions from these members as illustrated in FIG. 9A. In this case, the input member 122 and the output member 121 are engaged (locked) with each other via the rollers 123, and swing power of the input member 122 is converted into a rotational movement of the output member 121. Thereafter, when the rotational speed of the input member 122 falls below that of the output member 121 and the input member 122 swings in the idle direction relatively with respect to the output member 121, the input member 122 and the output member 121, which have been locked via the rollers 123, are unlocked, and the one-way clutch 120 is brought back to a free state (idle state) as illustrated in FIG. 9C.